Population-based surveys estimate that the prevalence of methamphetamine (meth) use is 20 times higher among men who have sex with men (MSM) compared to the general population. Meth-associated sexual risk behavior is also a driving force in the MSM HIV epidemic: meth use is consistently associated with high-risk sexual behavior and sexually transmitted diseases, including HIV. Despite these alarming data, relatively few interventions have been tested among meth-using MSM, and no studies have tested the efficacy of pharmacologic interventions in reducing meth use in this population. Pilot studies demonstrate that aripiprazole (Abilify), an FDA-approved, well-tolerated antipsychotic and partial dopamine agonist, reduces the effects of meth in humans, decreases meth craving, and exhibits an excellent safety profile. Partial agonists - - ligands with target receptor affinity but low intrinsic activity - - have already been shown to be effective in treating opiate and nicotine dependence. In response to the compelling evidence supporting aripiprazole and the partial agonist approach, we propose conducting a randomized, double-blind, placebo- controlled trial of intermediate size (60 participants) and length (90 days of follow-up) to assess the efficacy of aripiprazole in reducing meth use among meth-dependent, sexually active MSM. Our specific aims are: 1) To test the hypothesis that aripiprazole 20 mg daily will reduce meth use significantly more than placebo among meth-dependent MSM, as determined by the proportion of meth-negative urines and by self- report of meth use in the aripiprazole versus placebo group. 2) To measure the acceptability of aripiprazole and placebo among meth-dependent MSM, by determining (via electronic pill caps and self-report) medication adherence to aripiprazole and placebo. 3) To measure the safety and tolerability of aripiprazole and placebo among meth-dependent MSM, as determined by the number of adverse clinical events in the aripiprazole and placebo arms. All participants will receive HIV risk-reduction counseling and brief substance use counseling. If promising, we anticipate that study results will be used to design a phase III study to determine if aripiprazole's effects on reducing meth use lead to significant reductions in meth-associated sexual risk and, if the trial sample size is appropriate, HIV incidence.